This invention relates to an O-ring mounting groove to be formed in a shaft or the like, and a backup ring.
FIG. 6, shows an O-ring 2 and a backup ring 3, which are used for the purpose of sealing a shaft 1. These rings 2 and 3 are fitted into an O-ring mounting groove 4, the bottom surface of which is parallel with the outer periphery of the shaft.
In the example shown in FIG. 6, a rotation of the shaft 1 causes a torsional or a bending force to be generated, with the result that stress is concentrated on the O-ring mounting groove 4, which causes this groove 4 to become subject to distortion.
When distortion occurs to this section, stress is concentrated on a corner section 1a of the bottom of the O-ring mounting groove 1a, with the result that fatigue failure often occurs at this corner section 1a, where the shaft 1 will break. Thus, the conventional O-ring mounting groove has a poor fatigue characteristic, so that the service life of the shaft 1 is often very short.
Apart from this, the conventional backup ring 3 has the following problem: if the O-ring 2 is deformed by a pressurizing force applied thereto, part of the O-ring 2 can get into the gap between the backup ring 3 and the associated bearing 5, which will cause the O-ring 2 to break. Accordingly, the O-ring cannot enjoy a long service life.